Large Eddy Simulations of Supersonic Jet Flows for Aeroacoustic Applications (original) (raw)
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11th AIAA/CEAS Aeroacoustics Conference, 2005
Improvements in computing speed over the past decade have made Large Eddy Simulation (LES) an attractive tool to study jet noise. In addition, the study of turbulent hot jets for noise prediction is desirable compared to cold/isothermal jets since all jet engines fitted on aircraft operate at hot exhaust conditions. In this regard, we present results for two heated jets with temperature ratios of Tj/T∞ = 1.76 and Tj/T∞ = 2.70, respectively. A computational grid with approximately 4.8 million grid points is used the simulation. Spatial filtering is used as an implicit subgrid scale SGS model in place of the classical Smagorinsky and Dynamic Smagorinsky models. To study the far-field noise, the porous Ffowcs Williams-Hawkings (FWH) surface integral acoustic formulation is employed. The jet development results obtained using our LES methodology are consistent with other LES data and experimental results. The predicted OASPL values for our heated jets follow the trend measured by experiments though our results over-predict by approximately 3dB. Overall, our LES methodology coupled with the Ffowcs Williams-Hawkings aeroacoustics methodology provide satisfactory results.
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In this paper we consider the scattering of sound by two-and three-dimensional bodies with arbitrary geometries. Particular emphasis is placed on the methodology for the implementation of solid wall boundary conditions for high-order, high-bandwidth numerical schemes. The Impedance Mismatch Method (IMM) is introduced to treat solid wall boundaries. In this method the solid wall is simulated using a wall region in which the characteristic impedance is set to a different value from that in the fluid region. This method has many advantages over traditional solid wall boundary treatments, including simplicity of coding, speed of computation and the ability to treat curved boundaries. This method has been used to solve a number of acoustic scattering problems to demonstrate its effectiveness. These problems include acoustic reflections from an infinite plate, acoustic scattering from a two-dimensional finite plate and a cylinder, and acoustic scattering by a sphere and a cylindrical shell.
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High-fidelity large-eddy simulations (LES) are performed to investigate aeroacoustic characteristics of jets issuing from twin rectangular nozzles with an aspect ratio of 2:1 at two over-expanded conditions and the design condition. For all three jet conditions simulated, LES predicts qualitatively similar near-field flow statistics to those measured at the University of Cincinnati. Using the Ffowcs Williams-Hawkings method, LES captures the fundamental screech tone and its harmonics fairly well at multiple observer locations in the far-field. Intense jet flapping motions in the near-field along the minor axis, which are influenced by jet-to-jet interactions, are found to correspond to those frequencies. Moreover, the predicted overall sound pressure levels are within 1-2 dB of the experimental measurements. However, the screech tones appear to be intermittent, as the twin-jet interaction pattern varies irregularly. To extract dominant flow structures at the screech frequencies and identify the twin-jet coupling modes, spectral proper orthogonal decomposition (SPOD) analysis is used. SPOD analysis recovers energetic peaks at the screech frequencies, and the corresponding leading modes indicate strong upstream radiation originating from the fifth/sixth shock-cells. For the two over-expanded conditions, the leading modes show anti-symmetric coupling in the minor axis at the fundamental screech frequencies. In contrast, the two jets behave symmetrically with respect to each other in the major axis, in line with the absence of jet flapping in this direction. Furthermore, the leading SPOD eigenvalues turn out to be, at least, two orders of
Computational aeroacoustics and numerical simulation of supersonic jets
1996
In this paper we consider the scattering of sound by two-and three-dimensional bodies with arbitrary geometries. Particular emphasis is placed on the methodology for the implementation of solid wall boundary conditions for high-order, high-bandwidth numerical schemes. The Impedance Mismatch Method (IMM) is introduced to treat solid wall boundaries. In this method the solid wall is simulated using a wall region in which the characteristic impedance is set to a different value from that in the fluid region. This method has many advantages over traditional solid wall boundary treatments, including simplicity of coding, speed of computation and the ability to treat curved boundaries. This method has been used to solve a number of acoustic scattering problems to demonstrate its effectiveness. These problems include acoustic reflections from an infinite plate, acoustic scattering from a two-dimensional finite plate and a cylinder, and acoustic scattering by a sphere and a cylindrical shell.
Strong scaling of numerical solver for supersonic jet flow configurations
Journal of the Brazilian Society of Mechanical Sciences and Engineering, 2019
Acoustics loads are rocket design constraints which push researches and engineers to invest efforts in the aeroacoustics phenomena which is present on launch vehicles. Therefore, an in-house computational fluid dynamics tool is developed in order to reproduce high-fidelity results of supersonic jet flows for aeroacoustic analogy applications. The solver is written using the large eddy simulation formulation that is discretized using a finite-difference approach and an explicit time integration. Numerical simulations of supersonic jet flows are very expensive and demand efficient high-performance computing. Therefore, non-blocking message passage interface protocols and parallel input/output features are implemented into the code in order to perform simulations which demand up to one billion degrees of freedom. The present work evaluates the parallel efficiency of the solver when running on a supercomputer with a maximum theoretical peak of 127.4 TFLOPS. Speedup curves are generated using nine different workloads. Moreover, the validation results of a realistic flow condition are also presented in the current work.
Advances in computational aeroacoustics: challenges and issues
Needs of accurate and efficient numerical solvers in computational aeroacoustics have motivated the development of low-dispersion and low-dissipation schemes as an alternative to more classical methods of applied mathematics for computational fluid mechanics over the last two decades. These numerical methods have now reached maturity, even if progress is still necessary to take account of specific physics. The paper provides a short overview of some recent developments and applications involving these topics, and is organized as follows. Motivations and numerical advances are considered, but the main part of this synthesis focuses on the use of these simulations to improve our understanding of noise generation by turbulent flows. Applications to subsonic and supersonic jet noise, cavity noise and self-excited internal flows are thus presented.
Predictive Large Eddy Simulation for Jet Aeroacoustics–Current Approach and Industrial Application
Journal of Turbomachinery, 2017
The major techniques for measuring jet noise have significant drawbacks, especially when including engine installation effects such as jet–flap interaction noise. Numerical methods including low order correlations and Reynolds-averaged Navier–Stokes (RANS) are known to be deficient for complex configurations and even simple jet flows. Using high fidelity numerical methods such as large eddy simulation (LES) allows conditions to be carefully controlled and quantified. LES methods are more practical and affordable than experimental campaigns. The potential to use LES methods to predict noise, identify noise risks, and thus modify designs before an engine or aircraft is built is a possibility in the near future. This is particularly true for applications at lower Reynolds numbers such as jet noise of business jets and jet-flap interaction noise for under-wing engine installations. Hence, we introduce our current approaches to predicting jet noise reliably and contrast the cost of RANS–...
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Jet noise is still a distinct noise component when a commercial aircraft is taking off. A parallel high-fidelity simulation framework for industrial jet noise prediction is presented in this paper. This framework includes complex geometry meshing and Ffowcs Williams-Hawkings (FW-H) surface placement during preprocessing, a parallel hybrid RANS-LES flow solver coupled with an FW-H acoustic solver in the simulation and mean and unsteady data processing after the simulation. The use of this framework is demonstrated through two jet noise prediction cases: in-flight heated jets and installed ultra-high bypass-ratio (UHBPR) engines. These simulations can provide more insight than experimental tests into jet flow physics for engineering model improvement. Additional advantages are also shown in the cost and turnaround time. Thus there is great potential for high-fidelity jet noise simulations to partly replace rig tests for industrial use in the future.
Summary of “Supersonic Jet Aeroacoustics” Special Session
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